Coating zinc and the coated article



Patented June 8, 1937 PATENT OFFICE COATING ZINC AND THE COATED Matthew- Green, Detroit, Mich assignor to Parker Rust-Proof .Company, Detroit, Mich 'a corporation of Michigan No Drawing. Original application January 21,

1932, Serial No. 587,967. Divided and this application'octobcrz, 1935, Serial No. 43,198

This invention relates to coating zinc and to articles produced thereby andmore particularly to the acceleration of the formation on zinc of a coating of an approximatelyinsoluble salt ofzinc and other materials. vThis application is a diviof application Serial No. 587,967 filed Jan. 21,

It has long been known that a hot dilute solution of phosphoric acid acts on iron and, after sufiicient iron has been dissolved to fbalance the solution, a coating of comparatively insoluble phosphate is formed on the iron. This coatingis rust resistant and also makes an excellent foundation for paint or lacquer.

Similarly, a hot dilute solution of phosphoric acid will dissolve zinc untilit becomes balanced, and thereafter will form on zinc a phosphate coating. If the solution is previously balanced", the coating operation takes less time than when the start is made with the acid solution,- but it still requires an objectionably long time. The speed of. operation varies with the condition of the zinc surface, but one half hour is a fairly short time within which to secure a coating on zinc in a balanced zine phosphate bath.

I have discovered that the addition of iron to.

f the bath greatly accelerates its action, and also. improves the quality'of the resulting coating on the zinc, making it much more adherent. The

amount of iron in the bath may be varied widely.

The good effects of the iron increase with increase of the iron, at least until there is one half as much iron "as zinc dissolved in the bath. With sucha solution, a coating sufilcient for bonding paint may be produced-baa zinc surface in as little as thirty seconds, andis completed so that bubbling substantially ceases in from three to five minutes.

A solution may be 'used containing no zinc, if

40 preferred, the solution containing compounds of iron, or of iron and manganese. If manganese phosphate is used, there should be twice as much iron as manganese in the bath for best results;

" and the iron goes into the coating much more rapidly than the manganese, so that replenishment must be chiefly by iron, otherwise the manganese will soon become objectionably high. For this reason zinc phosphate wltha soluble compound of iron, sufilcient to furnish from one-third to one-half as much iron as there is zinc in the zinc phosphate, is preferred. A powder consisting of zinc dihydrogenzphosphate and a suitable" soluble compoundof iron is an advantageous form in which to sell and ship the necessary chemicals. Zinc can be coated with zinc salts of certain organic acids in a similar manner. These acids comprise the dicarboxylic and hydroxy-dicarboxylic acids in the aliphatic'series and carboxylic acids having but one carboxyl group and sulphonic acids in the aromatic series. In each case, the addition of a soluble compound of iron accelerates the action and-improves the resulting coating;

one'example of a very good solution for coating zinc is an aqueous solution of oxalic acid, sodium nitrate and sulphate of iron. It is preferable to use this solution as a spray. -It may be mixed with inert material, sprayed onto a -zinc surface, and dried thereon and then removed, or

it may be merely sprayed on as a liquid and the remnant washed off.

One specific mixture, with the inert material,-

which has been found satisfactory is: 1

Theox'alic acid; sodium nitrate and ferrous sulphate may be mixed in about the proportion specified and in the granular form, and dissolved in water to form the solution when desired. The

granular material may be shipped without pay-' ing freight on water, and still correct proportions insured.

A satisfactory liquid spray may be made by dissolving the same amounts of chemicals in 1 gallons water and omitting the fullers earth. Such a solution coats a zinc surface; even when at usual atmospheric temperature, and the action is very rapid. at a slightly elevated temperature. Other organic acids of the groupmentioned above may be substituted for oxalic acid, though most of them act'more slowly than oxalic acid and some require heating to produce results. Of these other acids, malonic, tartaric and gallic acids deserve special mention.

Other agents having a. similar oxidizing effect may be substituted for sodium nitrate. These include the various nitrates, nitrites, sulphites, etc., each of which has the desired oxidizing ef fect.

Other soluble compounds of iron may be sub-' stituted for the ferrous sulphate, the sulphate being cited because of its commercial availability.

If inert material is added, any other material having the necessary qualities may be substituted for fullers earth.

Apparently, in any case when a solution of a 2 y salt will react with ziricand iron, each separately, to produce a substantially insoluble salt on the surface of the metalkthe action of the solution on zinc is greatly expedited by the presence of a soluble compound of iron, and the resulting coating is improved in quality and adherence. An

article coated in this manner has a surface exceedingly well adapted to receive a finishing coat of paint, lacquer or enamel, and comprising apparently a substantially insoluble salt of zinc and a similar salt of iron. The above description explains-how this discovery may be utilized with various solutions and will be' understood as il-'- lustrati've rather than exhaustive, as the-inven-'- tion is capable of wide application within'the terms of the appended claims, in whichit will be understood that surfaceof zinc applies to the zinc coating on galvanized iron aswell as face comprising subjecting the said surface to the of "acid phosphate the step which comprises accelerating the action of said coating material by employing in the solution a soluble salt of iron.

3. A method of coating a metallic zinc surface which'consists in subjecting said surface to the coatingaction' of an acid zinc phosphate solution coritainin'g'dissolved inthe solution at least onethird as muchiron aszinc.

- 4. A method of coating a metallic zinc surface .which consists in subjecting the said surface to the coating action of an acid zinc phosphate solution and accelerating the action of said coating solution by employing in the solution a soluble salt of iron. J

5. A method of coating a metallic zinc surface which comprises subjecting the said surface to the coating action of an acid manganese phosphate solution containing dissolved in the solution a soluble salt of iron.

6. A method of coating a metallic zinc surface which comprises subjecting the said surface "to the coating action of an acid manganese phos- I phate solution containing,-dissolved in the solution, a soluble salt of iron, in which solution there is at least twice as much iron as manganese.

MATTHEW GREEN.

coating action of a coating material consisting 

